The relation between free will and physics is contentious and puzzling at all levels. Philosophers
have debated how free will can be explained with current scientific theories. There is debate
about the meaning of the term free will, even leading to questions about whether or not we have
anything called free will. A key focus of the philosophical debate is compatibility of free will
with deterministic physical theories. Philosophers who argue against determinism, suggest a
fundamental role for quantum theory in models of our decision making. It is the supposed link to
quantum theory first attracted my interest. The literature extends from philosophy journals to
science publications (Conway and Kochen 2006, Libet 1985, Nichols 2011).

This work takes a unique approach to the problem, looking for evidence, building models and
making predictions. It is critically important to recognise two different uses of the term free will.
An abstract concept, and a known property of human decision making, they are distinct and
require different approaches, but they are often confused. Searle (2007) points to the lack of
progress on the free will problem over centuries and suggests that the way forward will be to
recognise a false supposition. We identify that false supposition that: the phenomenon of free
will provides evidence and relevance for the abstract concept of indeterministic free will. It does
not.

There is an abstract concept of indeterministic free will. It is the concept of a decision making
process not governed by classical deterministic laws of physics. Because this is an abstract
concept, it makes sense to ask ‘Do we have free will?’ If we understand the concept then we can
design tests to answer the all-important question ‘Do we have free will?’ The answer might be
expected to depend on exactly how we define the conceptual form of free will. For the abstract
concept called free will we ask what its properties would be and how we could test for its
existence or measure it.

This paper also recognises a phenomenon of free will that we possess as a characteristic of
human decision making - a belief and common experience that we could do otherwise. It is
widely accepted, almost universal, and crosses cultural divides (Sarkissian et al 2010). It
underpins theological, legal and moral systems (Nahmias et al 2007), (Nichols and Knobe 2007).
The overwhelming majority of philosophers and commentators ascribe the property to humans,
generally not to animals, and most definitely not to computers. We will try to characterise and
model the phenomenon and then test the model against the facts. Note that the phenomenon of
free will (the phenomenon) exists, it is up to us to accurately model the phenomenon. We will do
exactly that.

This is not a review paper. Philosophical and other references are given to respected sources to
illustrate the debate, rather than as a comprehensive review. This paper is exclusively about the
decision making process. Some debate is about the ability or otherwise to enact a decision, where
an agent freely makes a decision but is impaired from acting on it by one form or other of
constraint (Frankfurt 1969). What happens after a decision is reached seems relatively free from
paradoxes and does not challenge the interface between the mind and the laws of physics.

In the literature the same term, free will, is used for the abstract concept of indeterministic
decision making and also for the phenomenon that we can do otherwise, which is a cause of
substantial confusion and is at the heart of most assertions that quantum theory is required to
explain free will. Some authors recognise the assumption they are making (Searle 2007), others
seem to make it unwittingly. Arguments along the lines of: free will [the concept] is
incompatible with deterministic laws; we have free will [the phenomenon] therefore it must be
due to non-deterministic theories, of which quantum theory is our prime example. Confusing the
two also takes away any motivation to look for evidence of the concept, because the
phenomenon is taken as that evidence. The confusion also undermines the search for models
because decision making that is indeterministic is equated to free will (the concept) without
explaining why that gives rise to perceived freedom to do otherwise, which is the phenomenon of
free will.

Hadley participated in a debate on free will at an organization called VVoIP_Physics_Debates. They are a non-profit, non-governmental organization formed to organize VVoIP (Voice and Video over IP) video-panel debates (seminars, colloquiums, workshops, and schools) supported by free of charge internet and paper publications of proceedings to facilitate progress in physics and related subjects.

The challenge model of free will aims to model the phenomenon of free will – the perception “that we could do otherwise”. Unlike two stage models it has nothing to do with determinism or indeterminism. The author, Mark Hadley, claims that there is no role for either determinism or indeterminism in explaining human free will. Not only is there no evidence for either, but any pattern of decision making could be replicated using either deterministic or indeterministic mechanisms.

The challenge model, is constructed from a standard goal seeking agent as commonly used in a variety of disciplines. A goal of “independence” is added. Independence is satisfied when the agent responds to a challenge. A challenge like “could you do otherwise” results in a probabilistic change in behaviour (the actual response depends upon all the other goals and states of the agent).

Furthermore, the agent can generate its own challenges “I wonder if I could do ….?” And therefore builds up a history of being able to do otherwise. That gives the perception to the agent, and to third parties, that they could do otherwise.

The clearest test of the challenge model is the way a very predictable action can be reversed in response to a challenge. Such as “could you write with your left hand?” “Could you put your hand near that flame?”